The algorithm that enables this optimisation represents a landmark achievement in the field of biomechatronics — the study of biology, mechanics, electronics and control.

"Existing exoskeleton devices, despite their potential, have not improved walking performance as much as we think they should," said Steven Collins, a professor at Carnegie Mellon University in the US.

"We have seen improvements related to computing, hardware, and sensors, but the biggest challenge has remained the human element. We just have not been able to guess how they will respond to new devices," said Collins.

During experiments, each user received a unique pattern of assistance from an exoskeleton worn on one ankle.

The algorithm tested their responses to 32 different patterns over the course of an hour, making adjustments based on measurements of their energy use with each pattern.

The optimised assistance pattern produced larger benefits than any exoskeleton to date, including devices acting at all joints on both legs.

"When we walk, we naturally optimise coordination patterns for energy efficiency. Human-in-the-loop optimisation acts in a similar way to optimise the assistance provided by wearable devices," said Collins.

"We are really excited about this approach because we think it will dramatically improve energy economy, speed, and balance for millions of people, especially those with disabilities," he said.